When using color concentrate the letdown ratio must match what is required for optimal coloring, for example 25 : 1 or 50 : 1. If the letdown percentage is low the color will not be dispersed adequately in the base resin. Also make sure that the correct size auger and settings are used with volumetric additive feeders. See Figure 22.2 for an example of a volumetric additive feeder. Different auger sizes will require adjustments to the feeder set point to achieve the correct letdown ratio.